The invention relates generally to the field of switches and similar devices used to control application of power to electrical loads. More particularly, the invention relates to the use of radio frequency identification (RFID) tags to indicate the state of an input device, such as a pushbutton, an electrical contact, a relay or contactor, and so forth.
In the field of electronics, a wide range of control devices is used for controlling the delivery of power to a load. Such control devices may include various switches, relays, contactors and disconnects to control load power, circuit breakers to protect electrical circuits from overload, and pushbuttons and selector switches to facilitate user control of power circuit operation. Additionally, a variety of electrical devices are known and currently available for indicating the state of a control device. For example, an auxiliary contact is often coupled to a contactor so that the auxiliary contact produces an auxiliary signal, a low power electrical signal that indicates whether the contactor is open or closed. The auxiliary signal may be coupled, as an input signal, to other components within a power control or monitoring system. For example, the auxiliary signal may be used to turn on or off an indicator light, or some other component within the power electronics system.
As power control systems and the logic required to control these systems become more complex, the number of state indicators increases, and the wiring coupled to the state indicators also increases. The increased wiring, in turn, leads to increased costs due to hardware requirements, connection labor and wiring maintenance. For example, control devices are often disposed within and on the doors of metal enclosures for load control purposes, with wires running between the door-mounted devices and internal devices. An increase in the number of wires increases maintenance problems due to wiring failure and inconvenient tethering of door-mounted devices with internal devices. Additionally, because there is a limit to how many wires can be placed under the common screw-terminal connectors, hardware is often added to control devices in the form of additional contacts driven by a mechanical or electromechanical shaft called an operator. Furthermore, each electrical connection creates the potential for vibration induced failure. Therefore, labor, maintenance and material costs could be reduced if the discrete wired state indicators could be replaced with wireless state indicators.
The use of wireless state indicators, however, presents the difficulty of finding a suitable power supply. Often times a power supply is not available from the control device. Even when power is available, in the form of load power, the conversion from high voltage to low voltage adds additional cost. Batteries, on the other hand, incur additional maintenance costs due to the need for frequent replacement, and large batteries may interfere with control devices housed within the limited space of the metal enclosures. Furthermore, power scavenging techniques (based on vibration, or light or thermal gradients) typically provide too little power to achieve suitable control update rates, are too large, or depend on unreliable sources.
Therefore, it may be advantageous to provide an improved state selection or indicator device. In particular, it may be advantageous to provide a state selection or indicator device that communicates wirelessly and employs a power supply that is reliable, maintenance free, and allows acceptable control update rates.